The present invention relates to a liquid crystal display device and, more particularly, to a transmissive type liquid crystal display device having very uniform display contrast ratio used in combination with such a projector as an overhead projector.
A usual film projector can project enlarged, changeable or moving images or pictures onto a display screen by using a liquid crystal display device instead of a transparency. By driving the liquid crystal display with electrical signals from a computer, television or other program sources, images or pictures to be projected can be changed electronically without exchanging fixed image transparencies as described, for example, at pages 161 to 162 of a textbook entitled "Fundamentals and Application of Liquid Crystal Electronics" edited by A. Sasaki, published by OHM Publishing Co. in 1979.
Also, instead of transparencies for an overhead projector, a liquid crystal display device can be used as disclosed in U.S. Pat. No. 3,844,650.
U.S. Pat. Nos. 3,731,986 and 4,653,861, for example, disclose liquid crystal display devices of a type which may be used instead of transparencies for an overhead projector.
FIG. 1 illustrates a projector system using a prior art type liquid crystal display device instead of transparencies.
Projector 1 comprises light source 2, condenser lens (Fresnel lens) 3, projection lens 9, mirror 7, display screen 8, and stage 10.
Liquid crystal display device 4 comprises housing 15 and liquid crystal display cell 14 having a thin film of twisted nematic material sandwiched between patterned transparent electrodes coated on opposing glass substrates with a pair of polarizers disposed outside the substrates as disclosed in the aforementioned U.S. Pat. Nos. 3,731,986 and 4,653,861.
The liquid crystal display device 4 is placed on the stage 10 of the projector 1 and creates the image to be projected onto the display screen 8 according to electrical signals from a computer, television or program sources.
In FIG. 1, light originating from the light source 2 is gathered and concentrated onto the liquid crystal display cell 14 by the condenser lens 3. The projection lens 9 magnifies and focus the liquid crystal image onto the display screen 8 via the mirror 7.
In the prior art projector system, light from the light source 2 is incident upon the liquid crystal display cell 14 at a angle varying according to the location in the liquid crystal area the light enters through the condenser lens 3 and this varying angle of incidence to the liquid crystal display cell 14 causes non-uniformity in optical contrast ratio in the image projected onto the display screen 8.